Is Vin Diesel playing Groot in Guardians of the Galaxy?

When it was first announced by Vin Diesel that he was going to have a meeting with Marvel, many assumed that the actor might be playing Vision or Ultron in THE AVENGERS: AGE OF ULTRON. According to Deadline though, Vin Diesel might actually be playing Groot in GUARDIANS OF THE GALAXY. This is based on a source for Deadline and the fact that Diesel posted this image yesterday of Groot as his cover picture for Facebook, although it has since been taken down.

With Deadline's source and Vin Diesel possibly teasing his involvement with GUARDIANS OF THE GALAXY on Facebook (he is pretty open/cryptic with his fans), there's a real good chance Diesel is voicing Groot in the film. I think a lot of us assumed he would play a bigger part in Marvel's cinematic universe (he still might - it's not like this has been confirmed), but if he ends up playing Groot in GUARDIANS OF THE GALAXY, I'd have no problem with that.